Hemispheric lateralization of functions related to emotion

Perceiver and poser asymmetries in processing facial emotion

This study examined both perceiver and poser asymmetries in processing facial emotion. Posers were left brain-damaged (LBD), right brain-damaged (RBD), and normal control (NC) right-handed males videotaped while expressing happiness and anger. Perceivers rated the facial expressions for asymmetry in original and reversed orientations. Overall, expressions viewed in the reversed orientation were rated as more left-sided than in the original orientation. In the reversed orientation, the more extensive left hemiface of the NCs and LBDs fell in the perceiver's left hemispace. This finding is consistent with previous research demonstrating a left hemispace bias for free-field viewing of emotional faces. Expressions were produced significantly more intensely on the left than the right hemiface by NCs and LBDs; expressions of RBDs were not significantly lateralized.

Affect, affective disorder and schizophrenia. A neuropsychological investigation of right hemisphere function

Performance on a happy-sad chimeric face test was used to examine the role of right hemisphere activation in positive and negative affect, both normal and abnormal, as well as in schizophrenia. This test is known to elicit a left-sided perceptual bias in right-handed normal subjects. Happy and sad mood in normals did not influence the perceptual bias. Depression and mania were associated with reduced and increased biases respectively, while schizophrenics showed no bias to either side. Possible explanations are right hemisphere hyperfunction in mania, moderate relative hypofunction in depression, and severe relative hypofunction in schizophrenia. The marked difference between mania and schizophrenia supports distinct pathophysiologies underlying the two conditions.

Hemispheric specialization for emotional expression: a reexamination of results from intracarotid administration of sodium amobarbital

Emotional and behavioral responses to sodium amobarbital injection were examined in 44 epilepsy surgery candidates. Thirty-three emotional reactions occurred in 26 patients, 44% of the reactions following right hemisphere injection and 32% after injection of the left hemisphere. Among all patients examined, laughter/elated mood was statistically more frequent following right hemisphere injection while crying was statistically associated with left hemisphere injections. These observed effects were not related to amobarbital dose, sex, bilateral hemispheric inactivation (angiographic crossflow), general cognitive status, or side of seizure onset. These results support differing specialization of emotional expression in the right and left cerebral hemispheres and their subcortical connections.

Psychophysiological correlates of human brain asymmetry: blood pressure changes during lateralized presentation of an emotionally laden film

Fifty adult subjects were shown an emotionally positive film either in their left or right hemisphere by means of a technique for lateralizing visual input that allows prolonged viewing while permitting free ocular scanning. It was found that the cerebral hemispheres markedly differ in their capability to regulate blood pressure during emotionally laden situations of a distinctly positive nature. Right-hemispheric film presentation caused a significantly higher increase in systolic and diastolic pressure than left-hemispheric viewing of the same film. Moreover, hemisphere asymmetries were further increased if lateralized stimulus presentation and the lateralized carrying out of a stimulus-related response were combined within the same hemisphere, thereby enhancing unilateral processing. Finally, males and females clearly differed with respect to interhemispheric regulation of blood pressure.

Toward a model to explain infant preferences by cerebral emotional asymmetry and hemisphere priming

This paper argues that the rightward preference observed in most infants can be described as the consequence of two characteristics of the human brain: (1) hemispheric asymmetry of processes underlying emotional experience and (2) priming of cerebral function. Ample research evidence supports each of these propositions, and they have gained increasing, though not universal, acceptance. In combination, they provide a sufficient explanation for several preferences which may have human survival value. They also produce several side-effects in human behavior which can be observed, but which appear to have no survival function.

Facial asymmetries in the spontaneous response to positive and negative emotional arousal

Facial asymmetries during emotional arousal were studied under conditions designed to produce spontaneous responses. Subjects who performed a difficult verbal task reported unpleasant emotions, tested high on state anxiety and showed greater changes in left than right-sided composite photographs compared to the relaxed state. Subjects who performed an easy version of the same task reported positive emotions, tested significantly lower on state anxiety and showed greater changes in right sided composites. The pattern of results is consistent with the lateralization of function for positive and negative emotions and not for cognitive task variables, however, a cognitive basis for these results cannot be categorically excluded. The role of arousal in the appearance of facial asymmetries is discussed.

Beyond scripts: a note on the capacity of right hemisphere-damaged patients to process social and emotional content

Individuals with right hemisphere damage (RHD) can comprehend simple scripts but have difficulties understanding more complex forms of discourse such as stories and jokes. This study sought to discover the point beyond simple scripts at which such patients begin to experience difficulties. Three-sentence, script-like vignettes which described everyday situations were created along two major dimensions: a social dimension (reflecting presence or absence of interactions between characters); and an emotional dimension (reflecting a positive, negative, or neutral emotion felt by a protagonist in the situation). Right hemisphere-damaged patients were asked to provide emotional characterizations of, and continuations to, these situational vignettes. Results indicated that individuals with right hemisphere damage were more likely than control subjects to attribute a positive emotional state to a character in a neutral situation. In other respects, there were no significant differences between RHD subjects and controls, although the RHD subjects made significantly more factual errors in their continuations than did control subjects.

Lateralization for the expression and perception of facial emotion as a function of age

In order to test the hypothesis of right hemisphere changes with age, this study examined lateralization for facial emotion in young, middle-aged, and older women (N = 90). For expression, subjects were photographed while posing positive and negative emotions. Composite photographs were created and rated for intensity. For perception, subjects were required to make intensity judgements about emotional chimeric faces. Overall, subjects demonstrated significant left-sided facial asymmetry for expression and significant left hemispace biases for perception. The findings for facial expression were not influenced by emotional valence or resting face asymmetries. There were no changes in lateralization as a function of age for either expression or perception. Taken together, these findings lend support to the notion that the right hemisphere mediates emotional processing across the adult life span.

Schizophrenia: a disease of interhemispheric processes at forebrain and brainstem levels?

The evidence is convincing that each human cerebral hemisphere is capable of human mental activity. This being so, every normal human thought and action demands either a consensus between the two hemispheres, or a dominance of one over the other, in any event integrated into a unity of conscious mentation. How this is achieved remains wholly mysterious, but anatomical and behavioral data suggest that the two hemispheres, and their respective bilateral, anatomical-functional components, maintain a dynamic equilibrium through neural competition. While the forebrain commissures must contribute substantially to this competitive process, it is emphasized in this review that the serotonergic raphé nuclei of pons and mesencephalon are also participants in interhemispheric events. Each side of the raphé projects heavily to both sides of the forebrain, and each is in receipt of bilateral input from the forebrain and the habenulo-interpeduncular system. A multifarious loop thus exists between the two hemispheres, comprised of both forebrain commissural and brainstem paths. There are many reasons for believing that perturbation of this loop, by a variety of pathogenic agents or processes, probably including severe mental stress in susceptible individuals, underlies the extraordinarily diverse symptomatology of schizophrenia. Abnormality of features reflecting interhemispheric processes is common in schizophrenic patients; and the 'first rank' symptoms of delusions or hallucinations are prototypical of what might be expected were the two hemispheres unable to integrate their potentially independent thoughts. Furthermore, additional evidence suggests that the disorder lies within, or is focused primarily through, the raphé serotonergic system, that plays such a fundamental role in consciousness, in dreaming, in response to psychotomimetic drugs, and probably in movement, and even the trophic state of the neocortex. This system is also well situated to control the dopaminergic neurons of the ventral tegmental area, thus relating to the prominence of dopaminergic features in schizophrenia; and the lipofuscin loading and intimate relation with blood vessels and ependyma may make neurons of the raphé uniquely vulnerable to deleterious agents.

Neuropsychological factors associated with perceptual biases for emotional chimeric faces

Mechanisms underlying hemispace biases for free-field judgments of emotional intensity in chimeric faces were explored. The Levy et al. chimeric faces task (1983b) was examined in relationship to relevant neuropsychological measures (emotional, imaginal, ocular). Forty-four normal adults were administered a test battery including measures of chimeric face perception, lateral eye movements to nonemotional and emotional instructions, image generation, and ocular dominance ("eyedness"). Overall, subjects showed a significant left-sided bias for judging chimeric faces and for producing lateral eye movements to emotional instructions. Asymmetries for chimeric face perception were significantly correlated with asymmetries for the location of self-generated images in space. When task modalities were examined, there was a specific relationship between chimeric face perception and tactile processing on the other neuropsychological measures.

Changes in perceptual asymmetry with the menstrual cycle

Changes in perceptual asymmetry between the premenstrual and postmenstrual phases of the menstrual cycle were assessed in 39 women. Perceptual asymmetry was measured with fused, single response dichotic listening tests. The usual right ear advantage (REA) for auditory language-related stimuli was significantly greater in the postmenstrual phase of the cycle. Subjects with repressive personality styles were less likely to show a change in REA with the cycle. These neuropsychological findings are related to previously described physiological and psychological features of the menstrual cycle and the repressive personality style.

Inducing emotion by unilateral contraction of facial muscles: a new look at hemispheric specialization and the experience of emotion

Subjects who maintained voluntary contractions of the left facial muscles experienced sadness. Right facial contractions resulted in a more positive but difficult to characterize experience. These contractions had similar effects on the affective tone of stories told about an ambiguous picture. These findings indicate that emotions can be aroused by unilateral muscle contractions without intervening cognitions. They provide a new methodology for studying the roles of the cerebral hemispheres in emotional experience. Finally, they support the conclusion that the right hemisphere is involved with negative emotional experiences and indicate that the left hemisphere is involved with experiences that are more positive but not readily characterized.

Perceptual asymmetry for happy-sad chimeric faces: effects of mood

Happy-sad chimeric face drawings were viewed in free vision by normal subjects. A significant and reliable perceiver bias toward the left hemiface when judging facial expression was found in right-handers whereas no consistent bias was found in non-right handers. This bias tended to be more pronounced in females. Subjects' current mood influenced their choice of facial affect but not their perceptual bias. In a further experiment, subjects were tested during induced elation and once more during induced depression. Again, though these moods increased the number of happy and sad choices respectively, the magnitude of the left hemifacial bias remained unchanged. The results are best explained by stable properties of the right hemisphere rather than arousal mechanisms. The implications of these findings are discussed in the light of the proposed hemispheric asymmetries in emotional perception and the possible lateralized effects of depressed mood on cognition.

Posed facial emotional expression in brain-damaged patients

Posed emotional facial expression was examined in brain-damaged adults with right (RBD) or left (LBD) hemisphere cerebrovascular lesions and in matched normal controls (NC). Subjects were videotaped while posing eight facial expressions (positive and negative) under two elicitation conditions (verbal command and visual imitation). Expressions were rated by four naïve judges for intensity, category accuracy, and valence accuracy. RBDs were significantly more impaired than LBDs or NCs on category and valence accuracy, while LBDs posed expressions with significantly more intensity than RBDs or NCs. These findings held for positive emotions only. The results for category accuracy replicate an earlier report (Borod et al., 1986) which utilized a different rating procedure. Finally, expressions posed to visual imitation were rated as more intense and more accurate than those posed to verbal command.

The right cerebral hemisphere: emotion, music, visual-spatial skills, body-image, dreams, and awareness

Based on a review of numerous studies conducted on normal, neurosurgical and brain-injured individuals, the right cerebral hemisphere appears to be dominant in the perception and identification of environmental and nonverbal sounds; the analysis of geometric and visual space (e.g., depth perception, visual closure); somesthesis, stereognosis, the maintenance of the body image; the production of dreams during REM sleep; the perception of most aspects of musical stimuli; and the comprehension and expression of prosodic, melodic, visual, facial, and verbal emotion. When the right hemisphere is damaged a variety of cognitive abnormalities may result, including hemi-inattention and neglect, prosopagnosia, constructional apraxia, visual-perceptual disturbances, and agnosia for environmental, musical, and emotional sounds. Similarly, a myriad of affective abnormalities may occur, including indifference, depression, hysteria, gross social-emotional disinhibition, florid manic excitement, childishness, euphoria, impulsivity, and abnormal sexual behavior. Patients may become delusional, engage in the production of bizzare confabulations and experience a host of somatic disturbances such as pain and body-perceptual distortions. Based on studies of normal and "split-brain" functioning, it also appears that the right hemisphere maintains a highly developed social-emotional mental system and can independently perceive, recall and act on certain memories and experiences without the aid or active reflective participation of the left. This leads to situations in which the right and left halves of the brain sometime act in an uncooperative fashion, which gives rise to inter-manual and intra-psychic conflicts.